Not saying this is your problem, but something to consider.
If tyres are left in the sun then they begin to form very fine rubber cracks in the sidewall rubber, these fine cracks allow moisture to migrate into the tyre along the carcass plies and the internal tyre belting. If fitted to a car then this isn't too much of a problem because as soon as you drive the car the tyre warms up and the moisture dissipates. If however the tyre is stored on the back of your 4wd or RV without a cover then tyre failure like this is common due to water ingress and steel belting corrosion within the tyre, like in the photo.
So, on our boat trailers if we store with the tyre in the sun and the tyre gets the fine sidewall cracks then when we go down the ramp with a warm tyre some of the salt water gets drawn into the tyre, being saltwater the corrosion happens quicker than rain water.
As I said, not sure it is in any way relevant to your failures but if you store your boat outdoors with a cover over it, then cover the tyres too.
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